In cellular mobile telephone systems and the like, with the aim of obtaining a high-speed and high-quality signal as well as increasing subscriber capacity, methods have been studied in which are formed, through the use of an array antenna reception device including a plurality of antenna elements, such directional patterns (beams) that cause the receive gain to increase for a direction from which a desired signal arrives and cause it to decrease for other directions. One of the methods is applied to a multibeam antenna reception device that selects a receive beam from a plurality of fixed directional patterns (multiple beams).
As an example of a conventional technique concerning the multibeam antenna reception device of this kind may be cited the one in which a receive beam with a delay path excellent in reception quality is selected from among a plurality of fixed receive beams for reception (see Patent Document 1).
In the following, the conventional multibeam antenna reception device will be described referring to FIG. 1.
FIG. 1 is a block diagram showing an example of the conventional multibeam antenna reception device.
The conventional multibeam antenna reception device comprises: a receiving array antenna 201; antenna 1 to N radio receiver sections 2031 to 203N corresponding to receiving antenna elements, respectively; receive beam 1 to M forming sections 2041 to 204M; and user 1 to L demodulation blocks 2051 to 205L.
The receiving array antenna 201 includes N (N: an arbitrary integer) pieces of the receiving antenna elements 2021 to 202N. The receiving array antenna 201 has no special limitation as to the directivity of the receiving antenna elements 2021 to 202N as a unit in the horizontal plane and the vertical plane. The antenna element may be of, for example, omnidirectional (non-directional) or dipole (bidirectional) type. N pieces of the receiving antenna elements 2021 to 202N are arranged in closely spaced relation so that signals received by the respective antenna elements correlate with one another. Incidentally, the receiving array antenna 201 has no special limitation as to the number of the receiving antenna elements and the arrangement thereof so long as N pieces of the receiving antenna elements 2021 to 202N are placed in the vicinity to each other. The receiving antenna elements may be arranged linearly or circularly with a spacing of one-half of the wavelength of the carrier frequency.
A signal received by each of N pieces of the receiving antenna elements 2021 to 202N contains a desired user signal component, a plurality of interference signal components and thermal noise. In addition, a plurality of multipath components are present in the respective desired user signal component and interference signal components. Generally, these signal components arrive from different directions. In other words, there exist plural pairs of receive beam numbers and desired user signal path delays.
Each of the antenna 1 to N radio receiver sections 2031 to 203N comprises a low noise amplifier, a band-limiting filter, a mixer, a local oscillator, an AGC (Automatic Gain Controller), an quadrature detector, a low pass filter, an A/D (analog to digital) converter, and the like. Taking the antenna 1 radio receiver section 2031 as an example, the section 2031 receives as input the output of the receiving antenna element 2021. The antenna 1 radio receiver section 2031 performs amplification, frequency conversion from radio to baseband, quadrature detection, analog to digital conversion, etc. for the input signal, and thereafter, outputs the signal to the receive beam 1 to M forming sections 2041 to 204M.
The receive beam 1 to M forming sections 2041 to 204M receive as input the output of the respective antenna 1 to N radio receiver sections 2031 to 203N. Each of the receive beam 1 to M forming sections 2041 to 204M forms a different fixed receive beam for the input signal to output it to the user 1 to L demodulation blocks 2051 to 205L.
Incidentally, there is no special limitation on the number and shape of the fixed receive beam as well as the method of forming the beam. In terms of shape, an orthogonal multibeam may be cited as an example of the fixed receive beam. Besides, as an example of the method of forming the fixed receive beam may be cited digital beam forming in which respective input signals are multiplied by a fixed complex beam weight by digital computation to obtain the sum thereof.
Further, with reference to FIG. 1, the receive beam 1 to M forming sections 2041 to 204M are arranged in the position subsequent to the antenna 1 to N radio receiver sections 2031 to 203N, and create beams for digital signals in the baseband. However, beam forming may be performed in the radio band with a Butler matrix.
The receive beam 1 to M forming sections 2041 to 204M forms different fixed receive beams, respectively, for all input signals containing the user signal component and the user signal multipath components to separate the signals according to the directions from which they have arrived.
Each of the user 1 to L demodulation blocks 2051 to 205L includes receive beam 1 to M path detection sections 2061 to 206M, a path delay/receive beam selection section 207, and a demodulation processing section 209.
In the following, the user 1 to L demodulation blocks 2051 to 205L will be described by taking one of them, the user demodulation blocks 2051, as an example.
The user 1 demodulation block 2051 receives as input the output of the respective receive beam 1 to M forming sections 2041 to 204M, and outputs a user 1 transmission beam number and user 1 receive data.
The receive beam 1 to M path detection sections 2061 to 206M receive as input the output of the receive beam 1 to M forming sections 2041 to 204M, respectively. Each of the receive beam 1 to M path detection sections 2061 to 206M detects user 1 signal path delay with respect to each input signal to measure the reception quality of the user 1 signal in the path delay, thereby outputting the result to the path delay/receive beam selection section 207. At this point, the respective input signals have been multiplexed by the user 1 to L signals and also by the multipath components of the respective user signals caused by propagation delay.
Incidentally, there is no special limitation on the method of multiplexing the user signal, and such signal multiplexing techniques as TDMA (Time Division Multiple Access) and CDMA (Code Division Multiple Access) may be applied. Further, there is no special limitation on the method of separating multiplexed user signals, the method of detecting the path delay of the multipath components, and the number of path delays to be detected. Still further, there is no special limitation on the index of the reception quality to be measured and the measurement method. Examples of the reception quality index include received power and SIR (Signal to Interference Ratio).
Besides, the receive beam 1 to M path detection sections 2061 to 206M may detect path delay and measure the reception quality of the user 1 signal in the path delay with only a known symbol (pilot symbol, etc.) of the user 1 signal.
The path delay/receive beam selection section 207 receives as input the output of the respective receive beam 1 to M path detection sections 2061 to 206M including a pair of a receive beam number and a path delay, and information on user signal reception quality in the pair of the receive beam number and the path delay. Based on the user signal reception quality, the path delay/receive beam selection section 207 selects a pair of a receive beam number and a path delay for use in demodulation, and outputs the selected pair and information on the user signal reception quality in the pair to the demodulation processing section 209.
A variety of methods may be applied to select a pair of a receive beam number and a path delay for use in demodulation without special limitations. For example, the top A (A: an integer not less than 1) pair(s) excellent in reception quality or at most B (B: an integer not less than 1) pair(s) meeting a certain standard of reception quality may be selected.
The demodulation processing section 209 receives as input the pair of the receive beam number and the path delay and the information on the user signal reception quality in the pair of the receive beam number and the path delay output from the path delay/receive beam selection section 207. The demodulation processing section 209 performs demodulation based on the input receive beam number and path delay to output the user 1 receive data.
With the construction described above, the conventional multibeam antenna reception device selects a receive beam, in which a delay path excellent in reception quality exists, from among a plurality of fixed receive beams for reception, thereby being capable of forming such beams that cause the receive gain to increase for a direction from which a desired signal arrives and cause it to decrease for other directions.
[Patent Document 1]
Japanese Patent Laid-Open No. HEI 11-266228